Abstract:Potential variation of thin oil film in electrolyte is an electrochemical process. Conductivity transformation mechanism of thin oil film in 5% Na₂SO₄ solution was studied by using multiple microelectrode array. It was pointed out that there existed electronic ionic transition of thin oil film in salt solution. At the early stage of immersion in electrolyte, the potential of thin oil film shifted positively varying with immersion time. With increasing of immersion time, when the potential of thin oil film reached most positive value, it began to shift negatively. Based upon general electrochemical theory for metal/oil/electrolyte system, an electrochemical analysis of potential variation of the thin oil film was presented. It was predicted that there were two kinds of film in the thin oil film, ionic and electronic conducting film. For the ionic conducting film, potential of thin oil film measured was equal to equilibrium potential of metal oxidation at metal/film interface (E ⁰ _a), and it had most negative value. For the electronic conducting film, potential obtained was equal to equilibrium potential of oxidant reduction at film/electrolyte interface (E ⁰ _c), and it had most positive value. It was suggested that the method of precisely measuring the potential of thin oil film in electrolyte utilizing multiple microelectrode array could be developed to study the conducting transformation mechanism of high resistance thin film in electrolyte.